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Author: Subject: High speed cameras
PHILOU Zrealone
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[*] posted on 17-7-2015 at 06:20
High speed cameras

When looking after slow motion camera, I found the following beast:
Phantom v2511 Camera

This could be used to analyse detonic processes in "slow motion" as it can go up to 1.000.000 frames per seconds...

It is of course out of budget reach for most of us :(.

If we take the VOD of 10 km/s as a typical example...this camera could take a picture for every centimeter of detonated explosive of a linear charge...If the detonation is slower then the frame can go above 1 picture/cm of detonating stuff.
The camera must be protected behind a shield.

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[*] posted on 17-7-2015 at 08:06

That would be cool but if you look deeper into the tech specs, you can only shoot 1M fps at a resolution of 128x16. I don't know if you'd be able to see much else other than VoD.

The V711 can do 1.4M fps but only at 128x8.

Where I work, we have a fleet of Phantom Miro M cameras for capturing airbag deployments. At 64x8, they can do 640k fps but that resolution is basically useless. We usually record at >5000 fps, since a typical curtain deployment takes anywhere from 18 to 35ms.

A LOT of light is needed to get this stuff on film, so we have whole electric panels just for lights. Some of these panels are 45kW, and they run banks of incandescent bulbs. Lately we have been switching to LED lighting which is much more efficient.

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[*] posted on 17-7-2015 at 10:28

A high speed camera of 2.5 million frames/second will be suitable for recording a detonating explosive charge. This what Army Research Laboratory (ARL) did. ARL scientists photographed a detonating explosive column boosted with PBXN-5 (95/5 HMX/Viton, also known as LX-10-0). From these rate sticks they were able to obtain detonation velocity in two way: one from the high speed photography and the other from the piezo pins (see Figure. 1) embedded in the rate stick at precise location. The detonation velocity obtained by the two method agree with one another within 2%.

Figure 1 (taken from [1]):

187001Pic1.png - 245kB

"A Cordin Model 570 digital high-speed rotating-mirror framing camera was used to image the detonation event Capable of up to 2.5 million frames/s recording speed, the Model 570 captures 74 independent frames at 4 Mpixels (2000 x 2000 pixels) resolution with dependent exposure times " see Figure. 5 (taken also from [1]):

920427pic2.png - 291kB

In a nuclear detonation event, high speed cameras have been used to capture the expansion of hot fireball. On such camera is the Rapatronic.

A nice video of a nuclear fireball expansion captured by Rapatronic camera (Rapatronic camera can take 50 million frames/second):


[1] Matthew M. Biss and Kimberly Y. Spangler, Detonation Velocity Measurements from a Digital High-speed Rotating-mirror Framing Camera, Army Research Laboratory, ARL-TN-0502, 2012.


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[*] posted on 17-7-2015 at 15:56

In case of a nuclear event, at least you don't need external lighting. :D

Speaking of light...sort of off topic, though very interesting talk:
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[*] posted on 20-7-2015 at 22:55

Alternative approach

Assuming 10,000 meters per second detonation rate , a 20 centimeter test sample of explosive is gone in 0.00002 seconds. A low cost digital storage oscilloscope attachment for a laptop computer with a 20 megahertz bandwidth and 0.000001 second per division timebase , having a sampling rate of ~ 50 Megasamples per second or better , is more than adequate to chart the detonation. See examples below

In the scheme depicted , a measured length of explosive is sandwiched between a sturdy metal base laid on masonry , and a strip of paper in contact with the layer of explosive which has been rubbed with a soft lead pencil ( No. 2 or a drafting B type ) to surface it with a uniform layer of graphite that appears like shiny gray metal. The explosive should be in direct contact with the penciled surface side on the paper without other intervening material. Upon initiation , the electrically conductive detonation front bridges the two materials in contact with the explosive completing an electric circuit. This detonation wave traveling from point ' A ' to point ' B ' reduces the conductive path of the graphite resistor the same as a tunable rotary pot variable resistor.

Measuring the resistance of the prepared paper resistor strip using an Ohmmeter one can obtain a baseline reading to compare and obtain a tunable rotary pot variable resistor to substitute in the test setup layout in order to calibrate the oscilloscope. It should be set to trigger recording a trace at the lowest available setting. Whether the screen trace will ramp up or down is a matter of choice since one can arbitrarily switch the signal so that it is inverted even post detonation working from the stored data and image of the trace. Dividing the length of the detonated sample by the horizontal time measurement directly tells you the velocity of detonation.

It is very important that the connection made to the metal busbar is at the opposite end to the connection with the resistor film , otherwise with both connections at the same end of the setup , the circuit loop will become smaller as detonation proceeds , augmenting the whole circuit induction which creates a surge of current. The battery in series provides the essential power and reference for measurement.


Detonation rate recorder.jpg - 19kB

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